Drawing of materials through reducing dies



Sept. 1, 1970 B. M. ARMSTRONG ET AL 3,526,115

- DRAWING OF MATERIALS THROUGH REDUCING DIES Filed Sept. 28, 1967 3 Sheets-Sheet 1 I N v E N T 0 R5 BRIAN MICHAEL flAMSTPONG Huaeew Mama/ms fi m Mme R N E Y5 Sept. 1,1970 5. M. ARMSTRONG T AL 3,526,115

DRAWING OF MATERIALS THROUGH REDUCING DIES Filed Sept. 28, '19s? 3 sheets-sheer z y w/KM ATTORNEYS Sept. 1,1970 a. M. ARMSTRONG ETAL 3,526,115

I DRAWING OF MATERIALS THROUGH REDUCING DIES Filed Sept. 28, 3 Sheets-Sheet 3 I 38 U U 39 F164. T

.INVENTORS Bem/v Mel/4E1. flkmrko/vq BY fllvo ew MIDDLE/W56 m I ATTORNEYS United States Patent U.S. Cl. 72-45 6 Claims ABSTRACT OF THE DISCLOSURE A wire is fed through a lubricant bath, a tubular seal, a chamber and a dieand draws lubricant from the bath into the chamber to build up pressure therein. A pump initially pressurizes the chamber to a high pressure value and is cut off when the pressure built up by wire movement reaches that value.

This invention relates to the drawing of materials through reducing dies.

According to the invention there is provided a method of drawing material comprising introducing the material to a die by way of a seal and lubricant pressure vessel, said seal being provided by a tubular member through which the material passes, and pumping lubricant into the vessel between the seal and the die at least during the initial period of the drawing operation, said material passing through the tubular member With a clearance sufirciently small to provide an effective seal against leakage of lubricant from the vessel.

According to the invention, there is also provided drawing apparatus comprising a die, a pressure vessel, and a seal, said pressure vessel'having an inlet through which lubricant may be pumped into the vessel between the seal and the die, said seal being provided by a member of tubular form which during use of the apparatus surrounds the material during its entry into the vessel to provide an effective seal against leakage of lubricant from the vessel.

Features and advantages of the invention will be apparent from the following description of embodiments thereof given by way of example only in conjunction with the accompanying drawings, in which:

FIG. 1 is a section through a wire drawing apparatus according to the invention,

FIG. 2 is a section through a tubular seal member of the apparatus of FIG. 1,

FIG. 3 is a section through a modified form of the wire drawing apparatus of FIG. 1, and

FIG. 4 is a layout of the complete wire drawing assembly.

Referring to FIGS. 1 and 2, the drawing apparatus comprises a high pressure die body 1, a central passage 2, a die 3, seal 4, a cooling coil 5 and a lubricant inlet 6 for feeding lubricant to the passage 2 between the die and seal. The die is held by a pressure plate 7 held by screwthreads 8, sealing between the die and body being provided at a line contact between a conical face 9 of the die and a shoulder 10 on the body. The seal 4 is likewise secured to and sealed against the upstream end of the body by a second pressure plate 7a screwthreadedly secured to body 1. Attached to pressure plate 7a is a pre-lubrication bath 12. In a variant apparatus, the coil 5 is omitted.

The seal 4 is provided by a member of tubular form, a major portion of the length of the central passage 4a of which is of constant cross-section. The bore of the "ice upstream region of the passage 4a increases in an upstream direction, the purpose of which will be described later on in the description.

One preferred method of operation will now be described.

Prior to wire drawing, lubricant is pumped under high pressure into passage 2, the tubular member of seal 4 surrounding the wire to be drawn with a small clearance to provide a seal against leakage of the lubricant from passage 2 between the wire and tubular member. Drawing is now commenced and lubricant is drawn into the tubular member and passage 2 from the pre-lubrication bath by the motion of the wire. The combined action of the shape of the central passage 4a of the tubular member and the motion of the wire result in the generation of pressure in excess of the pump pressure in passage 2 and the pump may now be shut off.

This method of drawing may be used eifectively on most types of materials, for example ferrous and nonferrous wire and rod and composite or so-called clad materials.

The operating pressure appropriate to a particular material may be controlled by varying the process parameters. Some examples of this are quoted in subsequent paragraphs. The pressures which can be sealed in the die unit, or alternatively which can be generated by the tube are controlled by the viscosity of the lubricant used and the dimensions of the tube relative to those of the wire. The lubricant may be any liquid of sufficiently high viscosity which retains its fluid characteristics at the pressures required. For example mineral oils (here the optional cooling coil may be utilised to cool the oil in the die unit to utilise its room temperature viscosity, for sealing purposes), glycerol, polyglycerol (proprietary brand GSC 90,000) may be used.

The dimensions controlling tube design are the length of parallel and the clearance between the wire and the tube. By way of example using GSC 90,000 (viscosity 750 stokes) the length of parallel may be 1 in., and the radial clearance between .001 in. and .004 in. Other di mensions may be found to be more appropriate where different lubricants are used.

The pressures employed to process any particular material are determined by the yield strength of the material and the type of surface finish required. For the most effective lubrication the pressure should be as high as possible consistent with the yield strength of the material being drawn. Where a highly burnished finish is required pressures below this level may be utilised. By way of example various materials have been processed effectively at the following pressures As an example of operating procedure the processing of predrawn 0.6% carbon steel wire will sufiice.

GSC 90,000 is used both in the pre-lubrication bath and in the pump. A 1 in. parallel x .002 in. radial clearance tube may be employed with a die to give a reduction in area of 30%. The wire is pointed to fit through the reduction die by conventional means. A forward tension is applied to the wire to effect a seal between the wire and the reduction die. Lubricant is fed into the die unit (from the pump) until a pressure of at least 50,000 psi. is attained. At this point drawing may commence and as 3 Wire speed increases, hydrodynamic pressure generation resulting from motion of the wire through the tube increases the pressure in the die unit to about 100,000 p.s.i. At this point (about 200 ft./min.) the pump may be switched 01f. Drawing speed may then be increased to any practicable level without deterioration in lubrication.

Feferring to FIGS. 3 and 4, a modified drawing apparatus comprises a die assembly having a body 21., a central passage 22, a die 23, seal 24, a cooling coil and a lubricant inlet 26. The die 23 is held by a pressure plate 27, secured by bolts 28, sealing between the die and body being provided at a line contact between a conical face 29 and a shoulder 30 on the body. The seal is likewise secured to and sealed against the upstream end of the body by a second pressure plate 270.

The cooling coil 25 has an inlet 31 and an outlet 32 and lies upstream of the lubricant inlet 26 and adjacent the seal.

The complete drawing apparatus includes a lubricant reservoir 34 (FIG. 4) incorporating a heater, such as a steam heater to raise the lubricant temperature and reduce its viscosity. A high pressure pump 35 will pump lubricant from the reservoir, through a pressure relief device 36 and a pressure gauge 37 to the inlet 26 of passage 22. The drawing die seal and body may be immersed in lubricant or as shown in FIG. 4 the die body may include a pre-lubrication bath 38 upstream of the seal and a cooling block 39 downstream of the drawing die.

The seal defines a conduit which will give a small clearance around the wire. The seal is of a hard wear resistant material such as tungsten carbide.

In operation wire 40 is pulled by any known method through the seal and then the drawing die, while lubricant, normally too viscous for pumping at the pressure required for effective lubrication of the reducing die, is heated in the reservoir to reduce its viscosity enough for pumping and is continuously pumped to the passage 22 where the lubricant surrounds the wire and is drawn by the wire into the drawing die.

Lubricant in the passage is at high pressure which may reach 60,000 p.s.i.g. and leakage of that lubricant through the seal 24 is effectively sealed by the higher viscosity lubricant in the region of the seal resulting from the presence of the cooling coil, the pressure drop across the seal, the clearance in the seal, the length of the seal and the speed of the wire passing through the seal.

When drawing mild steel wire of nominal diameter 0.115 inch suitable dimensions for the seal, are, bore 0.117 inch and parallel length 1 inch. A viscous oil is heated to a temperature of 75 C. in the reservoir 34 and pumped into the pressure vessel 21 at pressures of up to 60,000 p.s.i.g. The oil is cooled to about room temperature by the cooling coil 25 so that its viscosity is high enough to prevent excessive leakage through the tube seal 24.

Experimental work has shown that drawing force is about 30% less when drawing with lubricant injected at 40,000 p.s.-i.g. than when pressure is near zero. This indicates that lubrication is much improved at high lubricant pressures.

What is claimed is:

1. A method of drawing metal wire, comprising the steps of: introducing the wire to a die through a tubular seal and lubricant pressure vessel, pumping lubricant at a pressure equal to a significant proportion of the yield strength of the wire into the vessel between the seal and the die during the initial period of the drawing operation, feeding the wire at high speed through a prelubrication bath then through said tubular seal with sufficiently small but positive clearance through the tubular seal such that lubricant is drawn from the prelubrication bath, through said tubular seal into the vessel to generate hydrodynamically a lubricant pressure in the vessel in excess of the pump pressure, and stopping the pump when the generated pressure is at least equal to the pump pressure.

2. A method according to claim 1, wherein the lubricant is a mineral oil and including the step of cooling said lubricant within the vessel in the region of said tubular seal.

3. A method according to claim 1, wherein the lubricant has a viscosity of approximately GSC 90,000, wherein the tubular seal of 1" length and wherein the radial clearance between the wire and the bore of the tubular seal is between .001 and .004 in.

4. A method according to claim 3, wherein the lubricant is heated sufiiciently to facilitate pumping thereof into the vessel.

5. A method according to claim 1 wherein the pressure of said pumped lubricant is at least 40,000 p.s.i.

6. A method according to claim 1 wherein the material of said wire is selected from the group including ferrous and non-ferrous wire and rod and clad materials.

References Cited UNITED STATES PATENTS 1,896,674- 2/1933 Longwell 72-463 Re. 20,067 8/1936 Busey 72286 2,203,751 6/ 1940 Simons 7245 2,252,365 8/1941 Fisher 72-286 FOREIGN PATENTS 905,495 7 9/ 1962 Great Britain.

CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner US. Cl. X.R. 72463,467 

